Production of burr free aluminum parts



United States Patent 3,293,806 PRODUQTIGN 0F BURR FREE ALUli/HVUM PARTS John B. Holland, Birmingham, Mich, assignor to Ford Motor Company, Dear-horn, Mich, a corporation of Delaware No Drawing. Filed Aug. 12, 1964, Ser. No. 389,186

2 Claims. (Cl. 51320) This invention is concerned with a process for the machining of aluminum parts and is more particularly directed to the problem of producing final parts which are essentially free of burrs which are inevitably raised during machining operations.

This invention has found particular utility in the production of valve bodies for use in automatic transmissions for motor vehicles although the invention is by no means so limited. These valve bodies are small intricately machined aluminum castings. These castings are heavily machined and must be held to close tolerances. Many of the machined surfaces are located so that cleaning by conventional means such as wire brushing is impracticable.

The inherent characteristics of the aluminum casting alloys are such that it is not feasible to do the necessary machining operations without raising many burrs. The presence of these burrs in the finished casting cannot be tolerated because these burrs tend to become detached in service and to contaminate the hydraulic fluid with subsequent disruption of the valve action. These parts have been routinely anodized prior to the final cleaning operation to impart a protective surface to the casting.

This invention is predicated upon the discovery that burrs can be practically eliminated from the finished product if a double anodizing operation is employed. The castings as received are given a sand blasting treatment to remove dirt and the casting skin. These cleaned castings are given an initial anodizing treatment as the next step. This anodizing step is well known to the industry. The anodizing is conducted in a sulfuric acid bath at a temperature of 68 of 74 F. at a voltage of 12 volts and a time period of about 20 minutes. For a further discussion of the technical aspects of the anodizing of aluminum reference may be had to page 1801 of Third Edition of Chemical Engineering Handbook by Perry.

These initially anodized castings are now machined to the required finished dimensions. These machining op- 3,293,806- Patented Dec. 27, 1966 erations include the steps of milling, drilling, tapping, reaming, planing and honing. These machining operations raise burrs which are difiicult to remove. However the burrs raised after an anodizing treatment are appreciably harder and more fragile than those raised upon an unanodized article. After the machining operations have been completed, the article is again anodized. This final anodizing treatment renders the raised burrs very hard and brittle.

The preferred method of finally removing the fragile burrs is to expose the castings to a blast of abrasive particles propelled by a swiftly moving fluid. Commercially a shower of ground walnut hulls carried in a stream of air serves very satisfactorily. Use has also been made of a stream of fine solid abrasive particles such as sand propelled in a stream !of water. This is known as liquid honing. Either of these treatments are capable of removing substantially all of the burrs without extensive resort to tedious and expensive hand operations.

I claim as my invention:

1. The process of producing a burr free machined aluminum part comprising cleaning the stock from which the part is to be produced, anodizing the stock to produce a brittle surface at least in the areas to be subsequently machined, machining the stock to the final shape of the part whereby fragile burrs are produced, again anodizing the part containing the fragile burrs to further enhance the fragility of the burrs and finally removing the fragile burrs by an abrasive treatment.

2. The process of producing a burr free machined aluminum part comprising cleaning the stock from which the part is to be produced, anodizing the stock to produce a brittle surface at least in the areas to be subsequently machined, machining the stock to the final shape of the part whereby fragile burrs are produced, again anodizing the part containing the fragile burrs to further enhance the fragility of the burrs and finally removing the fragile burrs.

References Cited by the Examiner UNITED STATES PATENTS 2,040,715 5/1936 Smith 51-321 2,421,806 6/1947 Perry 51-320 LESTER M. SWINGLE, Primary Examiner. 

2. THE PROCESS OF PRODUCING A BURR FREE MACHINED ALUMINUM PART COMPRISING CLEANING THE STOCK FROM WHICH THE PART IS TO BE PRODUCED, ANODIZING THE STOCK TO PRODUCE A BRITTLE SURFACE AT LEAST IN THE AREA TO BE SUBSEQUENTLY MACHINED, MACHINING THE STOCK TO THE FINAL SHAPED OF THE PART WHEREBY FRAGILE BURRS ARE PRODUCED, AGAIN ANODIZING THE PART CONTAINING THE FRAGILE BURRS TO FURTHER ENHANCE THE FRAGILITY OF THE BURRS AND FINALLY REMOVING THE FRAGILE BURRS. 